The level of uncertainty is highest and, hence, risk of failing to achieve the objectives is greatest at the start of the project. The certainty of completion generally gets progressively better as the project continues.
Figure 2-2. Stakeholders' Influence Over Time
图2-2利害关系者影响随着时间的变化
Although many project life cycles have similar phase names with similar deliverables, few life cycles are identical. Some can have four or five phases, but others may have nine or more. Single application areas are known to have significant variations. One organization's software development life cycle can have a single design phase, while another can have separate phases for architectural and detailed design. Subprojects can also have distinct project life cycles. For example, an architectural firm hired to design a new office building is first involved in the owner's definition phase while doing the design, and in the owner's implementation phase while supporting the construction effort. The architect's design project, however, will have its own series of phases from conceptual development, through definition and implementation, to closure. The architect can even treat designing the facility and supporting the construction as separate projects, each with its own set of phases.
尽管许多项目生命期具有彼此相似的阶段名称，所要求的可交付成果名称也极其相似，但其内容绝少雷同。某些项目有4个或5个阶段，但另一些项目可多达9个阶段以上。即使在某单一应用领域内，也会有很大差别，如一个组织的软件开发生命期可能只有一个设计阶段，而另一个组织却可能将其分为功能设计和详细设计两个单独的阶段。项目内的子项目也可以有明显的项目生命期。例如，一家建筑师事务所受雇为他人设计新办公楼时，首先在设计时参与了业主的设计要求制定阶段，随后又在协助施工时参与了业主的实施阶段，协助施工。但建筑师本身的设计项目也有自己的一系列阶段，包括项目构思、要求制定、实施，直至项目收尾。这位建筑师甚至可以把办公楼的设计和对施工的协助视为两个不同的项目，分别包括各自的明显阶段。
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